1. Introduction In today’s scenario, cancer possesses a great threat to the universe which is spreading at a very faster rate in both developing and non-developing countries. There are achievements as well as the breakdown in context against the prevention of cancer across the world’s population. [1] The main target would be upon elementary prevention which could be subsidized permanently. It could become potent when the assets are limited and there is a huge divergence in the initial stage detection, screening, and anti-cancer therapies. [2] Across the world, there are 18.1 million of new reports registered and 9.6 million deaths due to 2 cancer have been reported in the year 2018 concerning various factors such as an increase in the population size, different age groups and the occurrence of cancer with sudden changes in the environment. The rate of occurrence and death rate of cancer varies accordingly for generations and countries. The major cause of death over 9.6 million human populations are dying from cancer every year across the world and there is a tendency of approximately more than 16 million cases registered every year to rise to 22 million cases by the next twenty years. The major prevailing cancers across the world are lung, breast cancer in females, prostate, and colorectal cancer across the world. The most frequently occurred and major cause of deaths is due to lung cancer followed by liver, stomach, lung, breast, and colorectal cancers. [3] There are diverse types of cancer-causing high-rate deaths i.e., prostate [4], breast [5], colorectal [6], lung [7], liver [8], thyroid [9] and pancreatic cancer. [10] It is increasing due to various factors such as alterations in genes, inherited genetic defects, age, gender, environmental exposure- UV rays, chemicals/ preservatives used in the food, radioactive materials, lifestyle and the variations leading to mutations. An approach for treating cancer clinically with chemotherapy [11, 12], radiotherapy [13, 14] chemically driven drugs [15], surgery [16] and certain inhibitors like vemurafenib against BRAF mutant skin cancer. [17] The studies have been reported that an immune system can trigger progressive tumors immediately irrespective of the virulent factors. In the renal and skin cancer, presence of tumor-infiltrating lymphocytes inside tumor which shows positive prognostic response, [18, 19] in colorectal cancer, CD8+ T cells shows positive prognostic response, in breast and ovarian cancer, tumor-infiltrating lymphocytes shows positive prognostic response. [20] Vaccines for cancer have a set of ways that need to be taken into consideration for creation, multiplication to promote immunity against tumors. In the last 100 years, more vaccines 3 being applied therapeutically to treat cancer and to achieve this target, control of tumour antigens, antigen-presenting cells and other immune signals of the tumour is been required. The combination of cancer vaccines with conventional therapeutic approaches may lead to remove regulatory adoptive T- cell suppression and improved clinical efficacy through costimulatory pathways. In particular, combination approach can lead to activation of the immune modulate cells by reboot of the immune system, and thus rendering tumor cells would be more susceptible to immune mediated killing. [21] 1. Mechanism of therapeutic vaccines for cancer The main objective of the vaccines against cancer is the activation of CD8+ cytotoxic T-cells as the ongoing research on mice upholds the therapy by these cells. The antigen presenting cells (APCs) capture the neoantigens from the vaccine and the dead cancer cells. Then, the activated APCs migrate towards the lymph nodes and MHC molecules exhibit the neoantigens to T- lymphocytes. The CD4+ T cells build up immunity contrary to cancers and CD8+ CTLs helps in the direct killing of the cancer cells by the degranulation process such as granzyme and perforin. [22] The peculiar type of vaccination approach is the activation of CD8+ cytotoxic T-cells linked with Major Histocompatibility Complex (MHC) class I. The vaccines have been categorized in the [Figure 1] according to their respective mode of action. 2.1 Peptide Vaccines in anticancer therapy The familiar way for the vaccination against cancer is the transmission of the MHC class I antigenic determinants from tumor associated antigens to stimulate CD8+ T cells duplicates that can work against self-antigens. [23] The peptides which are devised inside the adjuvants 4 like Montanide which is similar to IFA (Incomplete Freund’s Adjuvant) in the presence or absence of cytokines which includes Granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon ?, toll-like receptors which have shown feedback partially or completely in the different phases of clinical trials. [24] The vaccines with one or greater than one peptide can be infused with an adjuvant such as Montanide ISA-51, association with cytokines like GM-CSF to trigger antigen-presenting cells (APC). This adjuvant has triggered tumor associated antigens in particular cytotoxic T cells. The cancer vaccines undergoing clinical trials have been listed in Table 1.There is one burden as IFA can lead to the aggregation of T cells at the location of vaccination rather than promoting systemic immune response, peptide vaccines are generally approved; the adjuvants and assembly of cancer vaccines are still ongoing. The advantages of these vaccines are ease to access, economically available at mass level and ease in transportation due to its stability. [25] The second method that can show potent clinical effectiveness is the benefit of synthetic peptides which consists of MHC class I and MHC class II antigenic determinants. [26] The long peptide chains of length 23-45 amino acids infused subcutaneously proved efficient on an account of its processing and delivery pathway which leads to trigger of T-cells. [27] 2.2 Vaccines from Antigen Presenting Cells (APC) in oncoimmunity therapy The studies on the different sets of APCs such as activated B cells, peripheral blood mononuclear cells have shown great signs of progress and advancement. The dendritic cells have a mixed population of APCs aptly adopt antigens according to their environment. Further, they prepare and display these antigens to CD4+ and CD8+ T- cells and integrate immune response the signals to counteract upon the secretion of cytokines like interleukin 12 5 (IL-12) which alters it to type 1 immune response, tumor necrosis factor (TNF), interferon ?, IL-2 and it improves the stimulation of CD8+ cytotoxic T- cells. [28] 2.3 Vaccines from dendritic cells in tumor immunity The clinical trials of these vaccines have proved to be uncommon which involves ascertaining ways for vaccination. It is challenging to contrast clinical trials and analyze results regarding the efficiency of the trials. The tests have been performed on CD34+ progenitor cells, monocytes, tumor specific antigens, tumor associated antigens, MHC class I peptides. These vaccines are infused inside the patient’s body by mode of skin, blood and lymph nodes. The advantages of these vaccines are cost-effective, non- hazardous, shows good immune response as well as suppression of tumors can be seen in patients. The effective response of the clinical trials and immunologic has been shown by dendritic cells harmonized with Mucin 1 derived peptide and mixture of PADRE peptides infused through the skin in patients suffering from renal cell carcinoma. [29] The clinical trials performed on the patients with Skin and Thyroid cancer- MART-1, [17] Allogeneic tumor lysis, [30] Autologous tumor lysis, [31] Transfection with RNA, [32] Kidney cancer and Breast cancer- Vibrations with peptides, [33] Fusion of allogeneic dendritic cells with autologous tumor, [34] Multiple melanoma- Vibrations with Carcinoembryonic antigen (CEA) peptide, [35] Vibrations with mannan- MUCI fusion protein, [36] Modification in pox- virus encoding CEA with Tricom. [37] 2.4 Modified tumour- based Vaccines In the previous studies, mice were vaccinated with the destroyed tumour cells and transformed to show activation of immune cytokines like GM-CSF. [38] The major role is been played by tumor specific CTLs which investigates the cDNA libraries formed from 6 tumor cell derived mRNA and transfection takes place in the MHC molecule of the recipient. This can be achieved by focusing on the T-cell antigens, where the screening of peptides from MHC molecule takes place by the use of mass spectrometry and reverse phase- high performance liquid chromatography (HPLC). The development of vaccines established on autologous tumour cells is achievable but complicated. [39] 2.5 Cell Lines based Vaccines The tests have been performed on allogeneic cell lines in the presence or absence of autologous tumor cells. The tumor cells transfect to explicit increase in GM-CSF also known as G-Vax which serves as an ultimate boost in the study where the patients having pancreatic cancer obtains recombinant listeria bacteria signifies the tumor associated antigen mesothelin in presence or absence of G-Vax consisting of allogeneic pancreatic cancer cell lines. [40] Numerous vaccines are desirable without any hindrance from induced antibody and incorporation of bacteria present to act as abundant features of natural infection by activation of toll-like receptors and foreign pathogen receptors. [41] 2.6 Autologous tumor cell vaccines for immunotherapy The cells can be taken into an account for the transfection of antigen presenting cells such as autologous or allogeneic cell lines with the genomic DNA of tumour. In this way, the undefined mutated genes in particular to tumour can be manufactured and conferred for the trigger of the immune response. These vaccines are tedious to achieve from the patients who underwent surgery from a particular disease. The drawback is the production is limited to 2 to 3 dosage of vaccines from the autologous tumor and when there is availability of the autologous tumor, there is no consent about the processing, preservation, modification and delivery for a candidate vaccine. [42] 7 2.7 Virus mediated vaccines in oncolytic immunotherapy The vaccines used against human papillomavirus viruses such as Gardasil and Cervarix are certified against the virus intervened with cervical cancers in non- infected youths. Their performances take place by triggering humoral immunity in contrast to viral capsid proteins put together inside non- contagious viral-like particles. Adenoviruses can be treated as vectors precisely to vaccinate with tumor antigens by infusion inside the muscle tissue that can be efficiently transfected. [43] These viruses are used in- vivo to transform antigens into antigen presenting cells and every virus shows rare results on the transformed cells from triggering to suppression of cells. [44] The favourable approach that has been approved is GM-CSF acts as an adjuvant or as antigen-presenting cell transformed growth factor inside the herpes virus vectors. The commonly used vector such as T-Vec has been certified in patients against skin cancer in phase III trials. [45] The clinical trials performed on the patients so far, Skin cancer- Heterologous booster poxvirus tyrosinase, [46] Kidney and Colorectal cancer- Poxvirus encoded 5T4,[47,42] Heterologous booster poxvirus PSA and Tricom, [48] Poxvirus encoded Carcinoembryonic antigen and Tricom. [49] The other vaccines which had been gone through clinical trials on Skin cancer- NY-ESO-1 and Iscomatrix, [50] Ganglioside and Incomplete Freund’s Adjuvant, Lung cancer- ? Galcer PBMC with Interleukin-2 and granulocyte macrophage colony stimulating factor (GM- CSF), [51] Transduction of allogeneic tumor with antisense TGF-?2 , [52] Transduction of allogeneic GM-CSF mixed with autologous tumor, [53] Multiple melanoma- Umbilical vein endothelial cells, [54] Pleura cancer- Autologous tumor with GM-CSF, [55] Brain CancerTransduction of autologous tumor with antisense TGF-?2 ,[56] Head and Neck cancerHsp65. [57] 8 Certain more ways can be used as vaccines against cancer such as tumor ablation, where the removal of large and small tumors takes place. The radiofrequency ablation involves the heating at particular locations which leads to inflammation and necrosis, further shown to boost trigger activity of natural killer cells. [58] The cryoablation which involves the discharge of tumor associated antigens enhancing the immune response against tumors. [59] One example of the therapeutic vaccine against cancer is Sipuleucel-T produced by Dendreon which has been certified by the Food and Drug Administration (FDA). The therapeutic mechanism of the cancer vaccine has been shown in [Figure 2]. It is been authorized for metastatic prostate cancer on the analysis of 4.1 months progress in the long-term survival in phase III clinical trials. [60] 2. How a Cancer vaccine works? The definite responsive immunotherapy aims to trigger an immune response against tumor by transmitting the tumor antigens into dendritic cells and contributing the optimum requirements for the maturation of the dendritic cells inside an effective immune response of antigen-presenting cells. The four major ways for the working of cancer vaccines are [Figure 3] - identification of tumor- rejection antigens, stimulation of a robust host’s immune system, reducing the risk of autoimmunity, evasion of immune system. 3.1 Identification of tumour-rejection antigens The tumour antigens are extracted out from the cDNA library or from peptides that are removed from the top of the tumor cells identified as tumor specific cytolytic T-cells. The efficacy of the tumour antigens relies upon the prevalence and avidity of the T-cells present 9 inside the patient’s body. [61] The mode of interest of vaccination is with the designated antigens rather than few exceptions of genes, the antigens vary in their efficacy for achieving immunotherapy. Very less or no tolerance is observed in tumor antigens related to fetal genes observed in immunological sites like carcinoembryonic antigen (CEA) and MAGE family create great tumor-rejection antigens. In the case of tissue originated sites, MART1, ERBB2, SILV shows a bit of tolerance but uncertain tumor rejection antigens. [62] The major types of tumor antigens show strengthen with the description of Telomerase reverse transcriptase (TERT) acts as potent antigen in the patients suffering from cancer. Few other tumor antigens are Survivin and OFA; these antigens prove to be fundamental for safeguarding of oncogenic traits of the tumor cells where immune dodging can be hindered. [63] 3.2 Stimulation of a robust host’s immune system The objectives are to pathway tumour antigens inside the dendritic cells and further persuade the dendritic cells to discriminate into robust stimulation of immune response. There are two ways of dendritic cells pathway that is through in-vivo and ex-vivo. The in-vivo technique involves infusion of antigen combined with adjuvant inside the patient’s body; it is easily understandable and mostly favourable. In the case of the in-vivo technique, the dendritic cells are manipulated and loading of antigen will show the best distinction of action of the antigen presenting cells. The research study shows that dendritic cells- immunotherapy is efficient compared to other areas. The CD4+ T-cells act as providing immunity against tumour, cytokines like interferon ? helps in the stimulation of tumour cells towards CTL lysis enhancing MHC class I interpretation and internal pathway which triggers the innate arm of an antibody at the location of tumour and hinder angiogenesis. [64] The CD8+ T cells consist of the effectors’ arm of an antibody against the tumour reaction, from the information to reach an optimum result, CD4+ and CD8+ T cells are required to obtain immunity against tumour. [65] 10 3.3 Reducing the risk of autoimmunity Proper methods need to be followed for the vaccination against cancer to infuse a therapeutic antitumor response and avoid the undesirable height of autoimmune result. The peripheral immune system is been occupied by a range of autoreactive T- cells categorized into two different ways:-low avidity T-cells and low to high avidity of T-cells to tissue specific factors avoided by central and peripheral tolerance. In high avidity, autoreactive T-cells is prone to threat according to the facts. [66] 3.4 Evasion of Immune System The tumour cells generally promote the activation of STAT1 / B7H1 and secretion of IL-10, TGF-? factors that hinder the antitumor response. The genetic changes like mutations occurring in the tumour antigens make the tumour cells less viable to immune recognition leading to immune rescue. [66] The complication arises when the mutations appear to begin in the antigen processing pathway like proteosome, TAP, ?2- microglobulin. 3. Combination Therapy- Immunotherapy and Cancer Vaccines The sensible expansion of the vaccines and the immunotherapeutic ways for the medication of cancer involves the tumor microenvironment and immune response which determines the antitumor immunity. The suppression of regulatory T cells (Treg) build up danger for the patients to establish autoimmune diseases [Figure 4]. The consolidation approach of vaccines and immunotherapy brings about the stimulation of inhibitory pathways in the immunosuppressive microenvironment of tumor. There has been a positive report received for the consolidation therapy where it focuses on numerous arrays inside the immune system to increase immunity against tumor. An illustration where the efficiency of dendritic cells 11 vaccine against B16 skin cancer in the mice models can be raised by gene silencing of TGF?1 which decreases the regulatory T-cells associated with tumor. [67] The advantages of this consolidation approach hinder the immune checkpoints indicated in the research studies that blockage of PD1/PD-L1 pathway by anti PD-L1 to counteract the antibodies in combination with the exhaustion of regulatory T-cells to support relapse of disease. The blockage of the checkpoints has proved one of the best methods to suppress the tumor and work as a therapy against cancer. [68] The challenges faced in the development of cancer vaccines are the two major issues- tumor immune suppression and antigenicity. The obvious fact is the immune response of the healthy individuals and cancer patients works differently, so usually, the cancer patients have to negotiate in both the mechanisms of specific therapy and the tumor- specific. The antigenicity, where the vaccines don’t have a specific target to tumor antigens which leads to mutations due to certain factors such as lifestyle, genetic, and environmental sudden changes. [69] Nowadays, various new approaches are targeted towards immunotherapy and cancer vaccines which include the combination of checkpoint inhibitors and personalized neo-antigen vaccines. CTLA-4 plays a role to inhibit the stimulation of T-cell with the direct interaction of CD 80/86, where the T-cell activation is stopped and leads to no immune response. [70, 71] According to this statement, the blockage of checkpoints was done via the development of the monoclonal antibodies as an approach towards therapeutics. Ipilimumab, a FDA approved monoclonal antibody against CTLA-4 for the treatment of melanoma. [71, 72] In the previous research, it has been stated checkpoint inhibitors have shown up T-cell responses and tumours carry huge mutational stress which generates a lot of neo-antigens. [71] The melanoma and non- small lung cancer usually have a high load of neo-antigen which tends to 12 show positive feedback against checkpoint inhibitors and good overall survival rate. [72, 73, 74] On the contrary, tumours exhibiting fewer mutations such as thyroid cancer and leukaemia shows low overall survival rate. [75] Another approach regarding cancer immunotherapy is to release the immune response through inhibition of checkpoint molecules with use of inhibitors. Many of the patients wouldn’t respond well to immune checkpoint molecules, but they can benefit from the combination treatment of the inhibitors and antigen-specific therapy. CTLA-4, checkpoint inhibitor and Ipilimumab, the monoclonal antibody has been proved to lead NY-ESO-1 immune responses among the patients having prostate, ovarian cancer and melanoma. [76, 77] There have been reports where melanoma patients treated with NY-ESO-1 in combination with Nivolumab; PD-1 inhibitor showed 25% of the positive response among the patients. [78] 4. Future Perspectives of Combination Therapy The most challenging task is to analyze precise dosage and efficient response in the combination of various checkpoint inhibitors including CTLA-4 and PD-1. Different components have been implemented for the blockage of PD-1/ IDO/ CTLA-4 pathways which has shown encouraging results. This study can be taken into account by the combination of the targeted therapies of the immune response with conventional therapies [Figure 5] such as radiotherapy, chemotherapy and chemically driven drugs to see the response on the cancer patients. [79, 80] There are many issues which raise a concern about the type of antigen- whether tumorassociated antigens (TAAs) or neoantigens, in case of TAAs most commonly classified by 13 tumors but the limiting factor is the tolerance of the immune response whereas neoantigen are tedious, costly and difficult to know the tumor changes in a patient. There are clinical trials undergoing using a specific antigen for the vaccine but no one has checked the combined effect of TAAs and neoantigens on the activation of immune response. This can be studied further by future research. [81] Another aspect is the combination therapy which involves the right therapies involved altogether to have better results. It usually relies on the type of tumor, presence and the detection of biomarkers specific for patient. The use of vaccines applies as a last line option and to know the right time when to carry out the process. So, in order to apply this process, need to be sure about the dosage and the time for the immune response against the particular antigen. [82] Mostly the humans and animals have dissimilarities in their immune response, there are genetically engineered mice, xenograft and orthotopic models to avoid this complication. But sometimes, there is a demand for big animal models but it raises a concern for their breeding, ethical rules and housing. [83] 5. Conclusion To find a cure for cancer will be new sunshine for patients suffering from different types of cancer. The future lies in the use of this combination approach- cancer vaccines and immunotherapy together, where the danger of side effects is being reduced as compared with other therapies such as chemotherapy, radiotherapy, and certain drugs available in the markets. The chances of efficiency are increased as well as the survival of the patients suffering from cancer but more studies need to be performed to find a cure for the cancer. The combination of personalized therapies is making a new direction towards an 14 individualized patient’s immune response and microenvironment with new techniques for the treatment of cancer.